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    <title>Document</title>
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    <script>
        let str = 'abcdefghijklmn456'
        //let reg = /\d/g
        //console.log(str.replace(reg,'').split('').reverse().join(''))

        var arr = str.split('')
        let newArr = arr.filter(item => {
            return isNaN(Number(item))
        })
        console.log(newArr.reverse().join(''))
    </script>
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